The 2009 eruption of Redoubt Volcano continues. During the past week, growth of the lava dome within the summit crater has slowed based on observations of little change in dome shape. Using a Radarsat2 image from April 20 and thermal images obtained on April 16, the current dome is estimated to be about 500 m (1640 ft) by 700 m (2297 ft) and 150 m (500 ft) thick. Emissions of volcanic gases and minor amounts of ash continues. A probable rockfall from the lava dome generated a very localized dusting of ash early today. The aviation color code remains ORANGE and the alert level WATCH. AVO continues to monitor the situation closely and the observatory is staffed 24/7.

The last explosive event during the current eruption occurred on the morning of April 4 (05:55 AKDT). Since then, seismicity has remained elevated above background reflecting the ongoing process of dome growth and occasional rock falls. The nearly constant vapor and gas cloud rising above the volcano has remained mostly below 15,000 feet above sea level. Satellite images show thermal anomalies at the summit as well as the low -level plumes and sulfur dioxide clouds drifting away from the volcano. Airborne gas measurements on April 20 indicate that emission of sulfur dioxide and carbon dioxide has increased since the previous measurement on April 16.

On Tuesday, April 21, an AVO field crew repaired a GPS station at the research hut (webcam location) that had been damaged in the March 23 explosion. In addition, they retrieved data cards from other GPS stations and the Dumbbell Hills time lapse camera. AVO geologists sampled material from the last explosive event and lahar deposits in the Drift River Valley. Additionally, high-water marks were measured from the flow down Drift River on April 4. The flow averaged about 10 m (33 ft) in depth at mid-valley.

The current Redoubt eruption is expected to continue for weeks to months. During this time, a cycle of relatively quiet periods of lava dome growth followed by explosive episodes of dome destruction will likely take place. Future explosions pose an ongoing threat of lahars in the Drift River Valley, trace to minor ash fall throughout south-central Alaska, and ash-related impacts to aviation.

Heavily ice-mantled Redoubt volcano is located on the western side of Cook Inlet, 170 km (106 mi) southwest of Anchorage and 82 km (51 mi) west of Kenai, within Lake Clark National Park. Redoubt is a stratovolcano which rises to 10,197 feet above sea level. Recent eruptions occurred in 1902, 1966-68, and 1989-90. The 1989-90 eruption produced mudflows, or lahars, that traveled down the Drift River and partially flooded the Drift River Oil Terminal facility. The ash plumes produced by the 1989-90 eruption affected aviation and resulted in minor or trace amounts of ash in the city of Anchorage and other nearby communities.

AVO received no reports of activity at Cleveland during the past week. Satellite views of the volcano have been cloudy.

OTHER ALASKA VOLCANOES

Seismic activity is monitored in real time at 31 volcanoes in Alaska. Satellite images of all Alaskan volcanoes are analyzed daily for evidence of ash plumes and elevated surface temperatures. Some volcanoes may currently display anomalous behavior but are not considered to be at a dangerous level of unrest. Akutan, Aniakchak, Augustine, Dutton, Fisher, Fourpeaked, Gareloi, Great Sitkin, Griggs, Iliamna, Isanotski, Kanaga, Katmai, Korovin, Mageik, Makushin, Martin, Novarupta, Okmok, Pavlof, Shishaldin, Snowy, Spurr, Tanaga, Trident, Ugashik-Peulik, Ukinrek Maars, Veniaminof, Westdahl, and Wrangell volcanoes are in color code GREEN and volcano alert level Normal. All are at or near normal levels of background seismicity. AVO did not detect ash plumes or significant elevated surface temperatures in the vicinity of any volcano.

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.

VOLCANO ALERT LEVELS

NORMALVolcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

ADVISORYVolcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

WATCHVolcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway but poses limited hazards.

WARNINGHazardous eruption is imminent, underway, or suspected.

AVIATION COLOR CODES

GREENVolcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

YELLOWVolcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

ORANGEVolcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway with no or minor volcanic-ash emissions [ash-plume height specified, if possible].

REDEruption is imminent with significant emission of volcanic ash into the atmosphere likely OR eruption is underway or suspected with significant emission of volcanic ash into the atmosphere [ash-plume height specified, if possible].